Well the final trainer is already inserted, and you have to battle Mewtwo first in order to get to them. Assuming you are playing the Bug Fix and Final Trainer version, Mewtwo should now be standing on top of a ladder, and you can go up it once you beat him/catch him/etc.

Glaceon's TM list is just an oversight, I'll go back in and fix that. Also you should be able to catch Pikachu on Route 2 like in original GS, they just aren't very common.

I could go back and put those in. In the meantime though you can use an emulator like VBA Link or TGB Dual to trade and get them to evolve with the GTS on South Isle.

Adding in all of those other pokemon would take longer to bug test than adding in the final trainer (since the final trainer I could pretty much just resume from a couple of different post-kanto saves and make sure she worked lol) I might add them in the future, but right now I'm more focused on fixing bugs with what's there than adding a lot of new things. I have a lot of ideas, but I'm saving them for the Halloween Hack, which will be a prequel to this one and will hopefully be out in late October. But after that, there's nothing saying I can't go back and in a few more pokemon and things this coming christmas.

EDIT: I acutally thought about making Mewtwo the final trainer. But since I already had it so you could catch him, and wanted people's existing saves to make sense when they upgraded, I kept it as someone else. However the mewtwo as a final trainer idea could work in the prequel.